Only looking at your video once, I have a few suggestions.
I noticed that you tend to jump up at the conclusion of the shot. I could not tell if you are jumping up at contact with the ball or after because of the quality of the video. You must focus on staying down through the end of the shot.
From the back view, I saw your cradle hand tighten up significantly at the end of the shot, You start with a nice loose cradle, then at impact tighten up your hand. This can interfere with a straight stroke. Focus on keeping your backhand loose throughout the stroke.
Think about your natural rhythm, when you are shooting your best what is it. I saw you do well with 4 practice strokes. Then I saw a number of shots you missed where it looked to me like you one stroked the ball, then on the backhand view I saw a number of times you stroking 7-9 practice strokes, and missing some more. Find the rhythm that works for you and stick with it.
You may want to make this drill a bit easier on yourself by putting the balls closer together. Remember we all learn to crawl, and walk before we run. Look up progressive practice drills on this site. They are very effective, basically start out closer together with the balls, and then as you become proficient move them further apart. Also be more careful on the balls placement, try to line the balls up perfectly straight with the pocket. This way you will be able to tell a bit more about the quality of your stroke when you draw the ball back.
Hope this helps.